1. Technical Field
The present invention generally relates to a stereoscopic image display apparatus which tracks the position of an observer to generate a stereoscopic image.
2. Description of Related Art
Stereoscopic display is expected to be the mainstream among next-generation displays. An existing stereoscopic display presents images having parallaxes to a viewer, wherein the stereoscopic image effect is produced through the parallaxes. In a display, a time division multiplexing or a space division multiplexing may be adopted in order to give two eyes images of different parallaxes.
Regarding a stereoscopic display adopting the space division multiplexing, when an image is displayed, the resolution is usually evenly distributed to different views and multiple view images are displayed at the same time. Because different view images produce different parallaxes, the left eye and the right eye respectively receive images in different views and accordingly the stereoscopic image effect is produced. The more the views are, the more freely the observer is allowed to move. However, regarding a display having a fixed resolution, the resolution of a single view image is reduced when multiple view images corresponding to one single image are displayed. Thus, the number of views and the resolution cannot be taken care of together. Regarding a stereoscopic display adopting the time division multiplexing, based on the Visual staying phenomenon of the eyes, images in different views are sequentially sent to the left eye and the right eye within a short period (for example, 1/60 second) to achieve the stereoscopic image effect without reducing the resolution of the image. However, a broad bandwidth is required for playing the stereoscopic images because multiple view images need to be sent out within a short time.
The basic theory of visual effect of stereoscopic image will be described first. FIGS. 1A-1B are diagram illustrating the visual effect of a stereoscopic image. Referring to FIG. 1A, when a left eye 100a and a right eye 100b look at an object 102, a parallax is produced between the sight lines 104 of the left eye 100a and the right eye 100b and accordingly a stereoscopic effect is produced. Besides, because the two eyes have the same accommodation and convergence, a stereoscopic object is clearly presented.
Referring to FIG. 1B, when images corresponding to the two eyes are displayed through a flat panel display device 106, the accommodation of the sight line 104a of the left eye 100a falls on a position of the display device 106, and the accommodation of the sight line 104b of the right eye 100b falls on another position of the display device 106. Even though two different accommodations are produced by displaying plane images, the sight lines 104a and 104b are extended backwards into sight lines 108, wherein the intersection of the sight lines 108 is the convergence which is corresponding to the convergence of the actual object 102. Thus, a stereoscopic effect can still be produced by displaying plane images. However, since the accommodation and the convergence do not overlap, discomfort to the eyes may be caused.
FIG. 2 is a diagram illustrating a mechanism of a conventional stereoscopic image display apparatus. Referring to FIG. 2, two images 114a and 114b of an object 112 which have a parallax are respectively displayed on a display plane and provided to two eyes 100a and 100b. The parallax produces a stereoscopic visual effect of the object 112. However, as described above, discomfort may be produced to the eyes.
FIG. 3 is a diagram illustrating another mechanism of a conventional stereoscopic image display apparatus. Referring to FIG. 3, a single eye receives a plurality of view images so that problems caused by inconsistent accommodation and convergence are reduced. For example, a left eye 100a looks at two view images 114a and 116a in different views on a display plane, and a right eye 100b looks at two view images 114b and 116b in different views on the display plane. Thus, a virtual physical object 112 can be established. This technique requires images of high view density therefore is referred to as a supper-multi-view (SMV) display technique.
FIG. 4 is a diagram of the requirement and arrangement of view number according to the conventional SMV technique. Referring to FIG. 4, the distance between the pupils of two eyes is usually between 2 mm and 4 mm. If the distance between two pupils is assumed to be 65 mm and each eye receives at least two views, the widths of the views would be less than 2 mm. Accordingly, about 32 views are required. If the observer is allowed to turn his head, more views are required.
Many different designs have been provided in the conventional techniques. A method of scanning lenticular array devices by using laser is provided in U.S. Pat. No. 6,932,476, wherein each lenticular lens projects the light to a view. When the lenticular array devices are scanned, an image is displayed by using a liquid crystal display (LCD). Other views are produced by slightly displacing the lenticular array devices. Then, the light beam of the image is deflected by a light refraction device back to the perpendicular direction and enters the LCD to display images in different views. Through the mechanism described above, views of high density can be achieved and a high-density image display can be achieved.
A technique of projecting an image to a lenticular lens array screen by using a plurality of projects to increase the total pixel number of the image is provided in U.S. Pat. No. 6,999,071. Each lenticular lens of the lenticular lens array screen collects pixels projected by each of the projectors and distributes them to different parts in the space. As a result, the image is expanded horizontally and vertically by the lenticular lens array screen.
There are further different designs for displaying stereoscopic images, such as the U.S. Pat. No. 7,084,841 and 2002/0051118, etc. However, foregoing techniques respectively have their pros and cons due to the focuses thereof.